Method for direct reduction of iron ore using sleeve-shaped briquettes

ABSTRACT

A process for the direct reduction of iron ore utilizes sleeveshaped briquettes in a direct fired rotary table furnace. The briquette is formed of a mixture of iron ore, carbonaceous reductant, and a binder, compacted into the shape of an upright prismatic sleeve such as an annular cylinder or a block shaped sleeve. Vents or openings may be cut through the vertical walls. The bottom end of the briquette is notched or formed with feet or pads to enhance circulation of reaction gases when the briquettes are placed in an upright position on the table of a direct fired reduction furnace, and to support the briquette on the furnace table with a minimum of table contact area.

United States ate Harker et al.

[ 51 Nov. 25, 1975 [75] Inventors: Louis Meade Harker; Thomas Valle,

both of Carbondale, C010.

[73] Assignee: Jaconvel Company, Carbondale,

22 Filed: Aug. 16,1974

211 Appl. No.: 498,072

Howard et al. 75/28 Beggs et a1 75/36 Primary Examiner-M. J. AndrewsAttorney, Agent, or Firm--Burton, Crandell & Polumbus ABSTRACT A processfor the direct reduction of iron ore utilizes sleeve-shaped briquettesin a direct fired rotary table furnace. The briquette is formed of amixture of iron ore, carbonaceous reductant, and a binder, compactedinto the shape of an upright prismatic sleeve such as an annularcylinder or a block shaped sleeve. Vents or openings may be cut throughthe vertical walls. The bottom end of the briquette is notched or formedwith feet or pads to enhance circulation of reaction gases when thebriquettes are placed in an upright position on the table of a directfired reduction furnace, and to support the briquette on the furnacetable with a minimum of table contact area.

10 Claims, 11 Drawing Figures xx x x US. Patent Nov. 25, 1975 Sheet 1of3 US. Patent Nov. 25 1975 Sheet2of3 3,922,165

US. Patent N0v.25, 19.75 Sheet3qf3 3,922,165

llill IIIHI llllll METHODFOR DIRECT REDUCTION OF IRON ORE USINGSLEEVE-SHAPED BRIQUETTES BACKGROUND OF THE INVENTION The presentinvention relates to an improved process for the direct reduction ofmetallic oxides such as iron ore using sleeve-shaped briquettes in adirect fired furnace.

The term direct reduction refers to the conversion of iron ore,particularly in the oxide forms of hematite and magnetite, to free iron,at a temperature which is below the melting point of iron and, morespecifically, below the temperature of which large amounts of carbontend to go into solution in the metal which would result in theproduction of brittle pig iron.

Briefly outlined, the major steps in direct reduction processes comprisemixing the various ingredients, including iron ore, a carbonaceousreducing agent and a binder, and forming the mixture into pellets whichare fed into a reduction furnace wherein they are heated to reactiontemperature. The pellets are held in the furnace for a period of timesufficient to allow the reduction reaction to be substantiallycompleted. The reduced pellets, now containing substantial amounts offree iron, are cooled in a reducing atmosphere to prevent surfacereoxidation, and are then treated in any desired manner to place thefree iron in a form suitable for further use.

The direct reduction process for making iron and steel dates fromancient times. It was the only process known from at least as early as1400 B.C. until approximately 1350 A.D., when initial developments ofthe blast-type furnace began. With the advent of the hot blast furnacein England in 1819, the direct reduction process fought a losing battlewith the blast furnace, although direct reduction continued to bepopular in certain areas of the world, for example, in India andSwitzerland. Direct reduction is still used in the United States forspecialized purposes, such as for the making of powdered iron for thefabrication of sintered metal parts, but it is still generallyconsidered to be an uneconomical process for the mass production ofiron.

It is well known that direct reduction may be carried on or terminatedjust below the sintering temperature of the metal so that the size andshape of the ore pellets are largely preserved to form sponge iron. At ahigher temperature, the reduced iron fuses to form a pasty ball or massat the bottom of the furnace and, upon further working, becomes wroughtiron.

Two types of direct reduction furnaces have been in common use throughthe years. The first is the hearth or bloomery type furnace used in thiscountry until about 1901, and the other is the shaft type furnace inwhich the ingredients, namely ore, reducing agent, and flux, are chargedin layers in a vertical shaft. In both processes, the metal is recoveredat the bottom of the furnace in a pasty mass. Efforts to make the directreduction process economically feasible have not been limited to thesetwo types of furnaces, but have extended to most of the known types,including pot furnaces, reverberatory furnaces, regenerative furnaces,shaft furnaces, rotary kilns, retort furnaces and electric furnaces.

OBJECTS AND SUMMARY OF THE INVENTION The invention described herein isdirected to a direct reduction process utilizing an improvedsleeve-shaped 2 briquette. More specifically, the present inventionembodies the use of an improved briquette form which has been found tosubstantially enhance the economic value of the direct reductionprocess.

The principal object of the present invention is to provide a new andimproved direct reduction process for reducing iron ore to free ironutilizing an improved briquette form which increases the yield of freeiron in a direct reduction process.

A related object is to provide an improved process which enhances thedirect reduction reaction, provides for an optimum furnace load andincreases the furnace yield.

A briquette structure for use in the direct reduction method is formedof a mixture of iron ore, carbonaceous reducing agent, and binder, isshaped or formed into a prismatic sleeve, which is generally open ortubular in cross section, and includes radial ports opening through theside walls, as well as notches in the bottom or foot end. Such shapedbriquette structures can be placed in an axially upright position on thetable of a reaction furnace, which is preferably of the flat bed,direct-fired, rotary type. The briquettes are blanketed with flue gas atan inlet temperature of approximately 2300 F. for a reaction period ofbetween 30 and 45 minutes. Yields are substantially increased over theuse of solid pellets, which are generally spherical or ovoid in shape.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of one form of abriquette utilized in the present invention.

FIG. 2 is a bottom plan view of the briquette shown in FIG. 1.

FIG. 3 is a section view taken substantially in the plane of line 33 onFIG. 2.

FIG. 4 is a generally diagrammatic plan view of the table of a rotary,direct-fired, reduction furnace, showing an arrangement of briquettes ofthe type shown in FIG. 1.

FIG. 5 is an isometric view of a modified form of briquette embodyingthe present invention.

FIG. 6 is an isometric view of another form of briquette embodying thepresent invention.

FIG. 7 is a top plan view of the briquette shown in FIG. 6.

FIG. 8 is a side elevation view, with one side wall partially cut away,of the briquette shown in FIG. 6. FIG. 9 is a bottom plan view of thebriquette shown in FIG. 6.

FIG. 10 is a section view taken substantially in the plane of line 10-10on FIG. 8.

FIG. 11 is an enlarged fragmentary section view taken substantially inthe plane of line 11-11 on FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENT a. Ingredients Iron Ore Iron oreused in a direct reduction process is preferably of the type having ahigh iron content. Such ores are available naturally, or a relativelylow-grade ore can be readily beneficiated by any known beneficationprocesses. It has been found that an ore having an iron content of atleast 60% will give satisfactory results. Among the numerous ores whichhave been used successfully are a low-grade Republic ore which has been3 beneficiated to about 60% iron, such well-known ores as Silver City,Woody Creek, Mackay, Nevada Magnetite, Wilson No. l,Wilson No. 2, WilsonNo. 3, Empire, and many other ores, all of which contain or have beenbeneficiated to contain an iron content of at least about 60% orhigher.v

The selected ore is ground to a particle size of approximately 8 mesh orsmaller (-8 mesh). For example, it has been found that a particle sizeof about 35 mesh is suitable for most ores. The particle size to whichthe ore is ground depends primarily upon the particular ore selected.For example, a Silver City Ore ground to a particle size of 48 mesh gavegood results, whereas with a Wilson ore, a particle size of-l mesh gavesomewhat better results than when a slightly coarser particle was used.

The principal component of the iron ore is iron oxide. In mostinstances, this oxide is the magnetic iron oxide, Magnetite, althoughthe lesser oxide, Hematite, is not uncommon. Other ores such asTaconite, Limonite and iron pyrites and the residue known as Blue Billyfrom the sulfuric acid process, are useful. During the reduction processin the furnace, these oxides are reduced by reaction with a carbonaceousreductant to leave free iron.

b. Ingredients Reductant Carbonaceous reducing agents are well known inthe art. These reducing agents react with the iron oxides to remove theoxygen therefrom, ordinarily in the form of carbon monoxide and carbondioxide. Carbon monoxide, itself a reducing agent, will react furtherwith the oxygen in the ore to produce iron and carbon dioxide. Thelatter serves as an inert atmosphere surrounding the briquette, and maybe drawn from the furnace through a briquette cooling system to providean inert or reducing atmosphere therein.

Petroleum coke is one carbonaceous reducing agent found to be highlyadvantageous for reducing iron ore. This coke material is produced inconnection with the refining of crude oil. Heavy petroleum bottoms fromthe fractionation of crude oil are heated under such conditions as todrive off certain volatile components which are further processed intogasoline, leaving a solid residue known as petroleum coke. There arevarious ways of producing petroleum coke, one of which is known as a*fluid" coking process and another as a delayed coking process. Cokefrom both processes produces excellent results. Other types of petroleumcoke, coke produced from coal, and other carbonaceous substances mayalso be used to advantage.

The coke should be ground to a mesh size of 100 mesh or smaller (IOOmesh) and preferably in the range of about 100 to about -l50 mesh.

The amount of reductant employed should, in most instances, besufficient to completely reduce the iron ore. It has been observed thatusing 2 to 3% more than the theoretical amount required gives excellentresults. Ordinarily this amount of reductant constitutes between and byweight of the iron ore.

0. Ingredients Binder An appropriate binder is utilized to bind the ironore and coke in intimate admixture. It is desirable that a binder isselcted which enhances the reduction of iron ore to free iron. The basicingredients of one illustrative binder for this purpose are water, asoluble starch, and a soluble salt such as sodium chloride. A bindermade 4 up of these ingredients, compounded as herein described has beenfound not only to be effective as a physical binder but also to enhancethe subsequent reduction and produce an increased yield of free iron.

One starch utilized in the suggested binder is a conventionallaundry-type cooked starch. The preferable form of starch used is a typeof starch which dissolves in water when boiled to form a viscous,translucent liquid. The starch is used in the ratio of about 10 to about125 parts by weight starch to about 200 parts by weight of water.

As a further ingredient of the binder, there is preferably added a smallamount of sodium chloride, or com mon table salt, preferably in anamount of about 20 to about parts by weight of salt. The bindercompositions which I have found to be particularly useful areconstituted as follows:

The starch in powder form, and sodium chloride in granulated crystalform, are mixed with water. The mixture is brought to a boil and cookeduntil all the starch and sodium chloride have dissolved, and the mixtureappears as a viscous, translucent liquid. Alternatively, the starch andwater may be cooked, and then the salt added and the mixture boileduntil the salt has dissolved. One preferred binder composition comprises50 parts starch, 50 parts sodium chloride and 200 parts water. Thismixture is cooked until all the sodium chloride is dissolved, and themixture is a viscous, translucent liquid. Such a binder gives excellentresults when used in an amount equal to about 5% by weight of the ironore present in the briquette composition. It imparts a high greenstrength to the briquettes and after drying this binder provides a hardexterior shell on the green briquette which prevents crumbling.

d. Forming the Briquettes To form the briquette, the ingredients,including iron ore and the desired amount of the binder, for example 5%by weight of the iron ore, are placed in a mixer and the mass thoroughlystirred until the iron ore is completely wetted with the binder. Next, acarbonaceous reductant, such as petroleum coke, coal, or the like isplaced into the mixer in an amount equal to about 20% by weight of theiron ore, and the mixture is thoroughly stirred so that all particles ofiron ore and reductant are wetted with the binder. The mixing shouldcontinue until a substantially homogeneous mixture is obtained. Themixture is then formed into briquettes of the shape herein described inany suitable briquetting machine or by any appropriate method. Thebriquettes should be formed promptly to prevent the mixture from dryingout, preferably within A hour to 1 hour, at the maximum, after themixture is completed. If the mixture is stored in a tightly coveredcontainer, however, it may be kept in a useable condition for a numberof days.

The amount of binder employed will affect the time within which thebriquettes may be formed. In general, the use of an amount of binderequal to somewhere between 3 and 8% by weight of the iron ore has beenfound to provide for satisfactory binding of the briquettes withoutunduly restricting the time limits within which briquettes must beformed.

The temperature during the mixing operation is ordinarily roomtemperature, that is the mixing operation is carried out at temperaturesbetween 40 and 120 F. It is essential that during the mixing operationthe temperature be kept as low as possible to avoid unduly drying thematerial prior to forming the briquettes.

e. The Furnace In the furnace, which may be any conventional furnacesuitable for maintaining a reducing atmosphere, and a temperature in therange of 2lOO to 2400 F., the briquettes are heated to the temperatureat which the reduction reaction takes place. In general, with theimproved briquettes embodying the present invention as hereinafterdescribed, a furnace time of about 24 minutes at 2280 F. is appropriate.Depending upon the temperature, the briquettes will remain in thefurnace for a period of between about 20 and about 35 minutes. It willbe appreciated that the higher the temperature, the less the timerequired for the reaction to take place. The briquettes herein describedare especially suitable for use in a continuous, direct, gas-firedfurnace, wherein the briquettes are placed on a circular table whichslowly rotates through the furnace carrying the briquettes with it. Thebriquettes are placed on the table from an entrance chute, and after therequired period of time in the furnace, determined by the speed ofrotation or movement of the table, the briquettes are pushed off of orremoved from the table and directed into an exit chute from which theyare conveyed, through a cooling tunnel, to a finished product hopper.Gases from the furnace produced during the reaction may be pulled out ofthe furnace through the cooling tunnel by an appropriate exhaust fan.These gases are cooled in the tunnel, and, in turn, cool the exitingbriquettes. At the same time, these gases serve to help maintain anonoxidizing atmosphere in the cooling tunnel. The briquettes remain inthe cooling tunnel for a period of approximately minutes, or at leastfor a sufficient period of time to cool them to a temperature at whichthey will not oxidize in air, which temperature is generally 200 F. orbelow.

f. Briquette Structure and Reduction The briquette structure utilized inthe present invention, as shown in the drawings, comprises a generallyvertically upright prismatic sleeve structure in a variety ofconfigurations. The common features, however, to each of the modifiedconfigurations shown in the drawings are the upright structure, theapproximately oneto-one ratio of compacted reductant to vertically openpassages, and the minimum of foot or support area at the bottom of thesleeve structure for supporting the same on the furnace table.Additionally, transverse or radial passages may extend through the wallsof the briquette for further enhancing the circulation of reducinggases.

While a variety of shapes and configurations can be provided within thespirit and scope of the invention, two forms of the invention are shownin the drawings. In FIGS. 1 through 5 there is illustrated an uprightcylindrical sleeve having a single vertical passage therethrough. InFIGS. 6 through 11 inclusive, there is illustrated a generallyrectangular, block shaped prismatic sleeve structure in which there isprovided a plurality of vertical passages. Based on the latterconfiguration, a plurality of the cylindrical sleeves as shown in FIGS.1

6 through 5 could be bonded in close juxtaposition in a variety ofpatterns such as shown in FIG. 4.

The material to be reduced is compacted sufficiently to provide adequategreen strength for handling. The density to which the reductant iscompacted must be sufficient for that purpose, and yet not so tight ordense as to inhibit the reduction reaction. A variety of binders may beutilized as described above, as may a variety of forming processes andmolds.

A cylindrical sleeve from briquette embodying the present invention isshown at 10 in FIG. I of the drawing. Such a briquette comprises anupright, generally cylindrical sleeve, which is annular in crosssection, as shown'in FIG. 2, being formed by a cylindrical wall 11having an inner surface 12 and outer surface 13. The briquette sleeve 10is formed of a mixture of iron ore, carbonaceous reducing agent and abinder, as described above, and is shaped in an appropriate press undera pressure sufficient to compact the mixture to a density which providessubstantial green strength to the briquette. The briquette is thendried, and may be stored for later reduction in a direct-fired furnaceas described above.

The briquettes l0 embodying the structure above described areconstructed with a ratio of briquette height to outside diameter ofabout 5-to-3, and with a wall 11 having a thickness of between and about1 inch, and more particularly about l to about inch. A preferredbriquette sleeve structure is generally between about 4 inches and about6 inches high, and particularly about 5% inches high, with an outsidediameter of about 3 inches and a wall about 6 inch thick. In general, ithas been observed that the height-to-outside diameter ratio may varyfrom about I-to-l to about 2-to-l except that the proportion of thebriquette must be such as to insure an adequate central sleeve cavity.It is believed that it is desirable to maintain an internal diameter ofthe sleeve of at least about /2 inch in order that the furnace gases mayreach all areas of the briquette. Accordingly, the sleeve should beformed with a minimum internal diameter of about B inch in order toaccomplish this purpose.

Briquettes formed and shaped as described above have been found to behighly susceptible to direct reduction in a direct-fired rotary tablefurnace by arranging the briquettes in an axially upstanding postion onthe furnace table 15, as shown diagrammatically in FIG. 4. Thebriquettes may be arranged closely together on the furnace table asshown in FIG. 4, the void spaces centrally of the sleeves and betweeneach adjacent sleeve being sufficient to provide space for the reactiongases to substantially completely envelope the briquettes.

To further enhance the reduction reaction, and increase the circulationof gases about the briquette sleeves l0, notches 19 are desirably cut inat least the end 20 of the briquette 10 which is to be placed on thefurnace table 15. Additionally, radial holes 21 or apertures may be cutthrough the side wall 11 of the briquettes as shown in FIG. 5. Thesenotches and passages prevent the formation of pockets of gases withinand surrounding the briquettes adjacent the furnace table. Such notchesand passages are of greater importance in those briquettes havingsmaller internal diameters in order to insure effective contact by thefurnace gases. The reduction reaction thus proceeds completely anduniformly throughout the length and thickness of the briquette cylinders10.

The loading pattern of briquettes 10 on the furnace table depends inpart on the table configuration. Where the furnace embodies a rotarytable, the briquettes may be loaded either radially, or in a sectionalpattern as shown in FIG. 4 to facilitate maximum table utilization. Toload the furnace with an array of cylindrical briquettes 10, forexample, the briquettes may be placed on a sectorshaped loading chute l6and deposited on the furnace table in a group through an entrance doorof the furnace. As the table 15 rotates through the furnace, thebriquettes are reduced. Following reduction, the briquettes are removedfrom the table by a scraper 18 or other appropriate removal mechanism.After being cooled, the briquettes may be crushed and the ironmagnetically separated from the remaining ingredients.

Another form of briquette shaped as a generally rectangular prismaticsleeve structure, is shown in FIGS. 6 through 11. Referring to thesefigures of the drawing, the prismatic sleeve shaped briquette, showngenerally at 30, comprises a generally rectangular block having sidewalls 31, end walls 32 and intermediate walls, indicated generally at34, defining a plurality of vertically extending passages 35. In theform shown in the drawings, the intermediate walls 34 include a singlelongitudinal wall or web 36 extending between the end walls 32 andgenerally parallel to the side walls 31, and a plurality of intermediatetransverse walls or webs 38 extending generally parallel to the endwalls 32 between the central longitudinal wall 36 and the outer sidewalls 31. In this manner, an array of vertically extending passages orsleeve openings 35 are defined extending between the upper surface 39and the lower surface 40 of the prismatic block 30. The briquette 30 issupported on its bottom surface 40 on a furnace table. To facilitate thepassage of gases upwardly through the passages 35 and to minimize thearea of contact between the block and the furnace table, a plurality ofnotches 41 are defined in the outer side walls 31 and the intermediatewall 36. Additional notches may be formed in the end walls 30 andintermediate walls 38 if desired. In this manner, the area of contactbetween the bottom surface 40 of the briquette and the furnace table isminimized.

Referring to FIGS. 8 and 10, to facilitate molding the briquettes, thevarious walls of the briquette taper from the upper surface to the lowersurface. The material to be reduced is compacted into a mold definingthe shape of the briquette and after appropriate green cure, thebriquettes are removed from the mold for use in a recuction furnace.

The prismatic briquettes, in one preferred form, are inches long, 8inches wide and 8 inches high, with 14 core passages therethroughdefined by exterior walls which taper from a width of inch at the bottomof the briquette to 5/16 inch at the top of the briquette and interiorwalls or webs which taper from inch at the bottom of the briquette to 1%inch at the top of the briquette. The vertical, open passages thusformed have a dimension tapering from 2 X 2 /8 inches at the bottom ofthe briquette to 1% X 2% inches at the top of the briquette. It can beobserved that the volume of compacted reductant material to the volumeof the vertical passages is approximately l-to1, and, with thedimensions given, the volume of reductant material in the briquette, asshown in the drawings, is 56% of the total volume of the briquette.Depending upon the dimensions utilized for the walls of the briquette,the percentage of reductant material by volume can be expected to runbetween 45 and 65percent by volume of the briquette. It must be kept inmind that the burden of actual quantity of reductant material on thefurnace table must be sufficiently large to make the process aneconomical one, and yet the reductant material must be shaped in such amanner as to maintain open and un burdened a substantial area of thefurnace table. Also, adequate provision must be made for circulation ofreducing gases throughout and around the briquettes in order to insureuniform reduction of the reductant materials. This is accomplished bythe notches in the bottom walls of the briquette and additionallyapertures may be provided through the various walls of the briquette tofurther facilitate circulation of the reduction gases.

It has been observed that the use of the prismatic, sleeve-shapedbriquettes aligned with the briquettes standing axially upright on afurnace table, so that the open passages extend from the top to bottom,prevents the smothering of briquettes and exclusion of certain portionsthereof from the furnace gases. These gases are apparently important inthe reduction reaction process, as it has been observed that when alayer of more than one thickness of pellets or ovoid briquettes isutilized on the furnace table, the briquettes adjacent the table areincompletely reduced. By utilizing the sleeveshaped briquettes 10 in anaxially upright position, the load of iron ore containing mixture perunit area of the table can be substantially increased, and at the sametime there results a highly efficient and complete furnace reactionthroughout the entire length and thickness of each briquette.

As described above, the briquettes are heated in a direct-fired furnaceand are contacted directly with the furnace gases. It is essential thatthe furnace gases surround and intimately contact substantially all ofthe briquette surfaces in order that the reduction reaction proceeduniformly throughout the briquette. Obviously, the portion of thebriquette contacting the table cannot be surrounded by the flue gas;however, by utilizing briquette sleeves with notches cut in thesupporting end surface, ample opportunity is given for completecirculation of the flue gas and reaction gases around the briquettes.Thus the briquettes react uni formly throughout their length andthickness.

It has been observed that briquettes of the abovedescribed proportionsproduce highly satisfactory results. Moreover, it has been observed thatby the use of briquettes having the shape and configuration embodyingthe present invention furnace production is increased approximatelythreefold. In one operation, for example, where the furnace was capableof lbs. per hour of reduced product utilizing pellets, this produc' tionrate was increased to 240 lbs. per hour through the use of briquettesembodying this invention. It has been further observed that the use ofthe sleeve-like briquettes prevents the furnace hearth from beingsmothered and cooled.

Referring to FIG. 4, it can be seen that the entire furnace table areais not covered. Sufficient uncovered table area remains centrally of thebriquettes and between adjacent briquette which is exposed to hotfurnace gases to maintain the table surface at the desired temperature.In this manner, the furnace table or hearth maintains its heat, therebyresulting in a conservation of fuel energy in the process.

While illustrative embodiments of the present invention have been shownin the drawing and described above in considerable detail, it should beunderstood that there is no intention to limit the invention to thespecific forms disclosed. On the contrary, the intention is to cover allmodifications, alternative constructions, equivalents and uses fallingwithin the spirit and scope of the invention as expressed in theappended claims.

We claim as our invention:

1. A method of producing iron by the direct reduction of iron ore,comprising the steps of forming a prismatic sleeve-shaped briquette froma mixture of iron ore having an iron content of at least about 60% and aparticle size of about 8 mesh or smaller, a carbonaceous reducing agenthaving a particle size of 100 mesh or smaller in an amount of betweenabout and about by weight of the iron ore, and an aqueous starch basesodium chloride containing binder in an amount of between about 3 andabout 8% by weight of the iron ore, with said sleeve-shaped briquettehaving at least one generally vertical passage therethrough, and saidbriquette further having defined in at least one end thereof a pluralityof notches; arranging a plurality of said sleeve-shaped briquettes on amoving table of a direct-fired furnace with said briquettes arranged inan axially upright position and with the notched ends thereof on saidtable and with the passage extending vertically upwardly; and subjectingsaid briquettes directly to furnace gases at a temperature of betweenabout 2000 and about 2400 F. for a period of time between about 20 and35 minutes, thereby to directly reduce a substantial portion of themetallic iron oxide to free iron; while said moving table carrying saidbriquettes slowly rotates through the furnace and removing said reducedbriquettes from said furnace and cooling the briquettes to a temperatureof about 200 F. or below in a nonoxidizing atmosphere.

2. A method as defined in claim 1 wherein the volume ratio of reduciblemixture to open passage in said shaped briquette is about l-to-l.

3. A method as defined in claim 1 wherein the proportion of reduciblemixture in said shaped briquette is between about 45% and about 65% byvolume.

4. A method as defined in claim 1 wherein said shaped briquettes includea plurality of apertures cut radially through the walls of eachbriquette intermediate its ends.

5. A method as defined in claim 1 wherein each said prismaticsleeve-shaped briquette is annular in cross section.

6. A method as defined in claim 1 wherein each said prismaticsleeve-shaped briquette is generally rectangular in cross section.

7. A method as defined in claim 1 wherein each said sleeve-shapedbriquette comprises a generally cylindrical member having aheight-to-outside diameter ratio of between about l-to-l and about2-to-l an inside diameter of at least about inch, and a wall thicknessof between about inch and about 1 inch, and said member having definedin at least one end thereof a plurality of radially extending notches.

8. A method as defined in claim 1 wherein each said sleeve-shapedbriquette comprises a generally rectangular member having a plurality ofvertically extending passages extending therethrough between the top andbottom thereof, said member having a volume ratio of reducible mixtureto passage volume of about l-to-l and a wall thickness of between aboutinch and about 1/18 inch, and said member having defined in one endthereof a plurality of notches extending through the member walls.

9. A method of producing free metal by direct reduction of a mixturecontaining a metallic oxide ore, comprising the steps of forming aprismatic sleeve-shaped briquette from a mixture of metallic oxide ore,a solid reducing agent and a binder, with said sleeve-shaped briquettehaving at least one generally vertical passage therethrough, and saidbriquette further having defined in at least one end thereof a pluralityof notches; arranging a plurality of said briquettes on a circular tableof a direct-fired furnace with said briquettes in an axially uprightposition, with the notched ends thereof on the furnace table, and saidpassage extending vertically upwardly; and subjecting said briquettesdirectly to the furnace gases at a temperature below the sinteringtemperature of the free metal for a period of time sufficient tosubstantially reduce the metallic oxide to free metal while saidcircular table carrying said briquettes slowly rotates through thefurnace.

10. A method producing free metal by direct reduction of a metallicoxide ore as defined in claim 9 including the step of cooling thedirectly reduced briquettes in a nonoxidizing atmosphere to atemperature below that at which the free metal will be oxidized in air.

1. A METHOD OF PRODUCING IRON BY THE DIRECT REDUCTION OF IRON ORE,COMPRISING THE STEPS OF FORMING A PRISMATIC SLEEVESHAPED BRIQUETTE FROMA MIXTURE OF IRON ORE HAVING AN IRON CONTENT OF AT LEAST ABOUT 60% AND APARTICLE SIZE OF ABOUT 8 MESH OR SMALLER, A CARBONACEOUS REDUCING AGENTHAVING A PARTICLE SIZE OF 100 MESH OR SMALLER IN AN AMOUNT OF BETWEENABOUT 15 AND ABOUT 20% BY WEIGHT OF THE IRON ORE, AND AN AQUEOUS STARCHBASE SODIUM CHLORIDE CONTAINING BINDER IN AN AMOUNT OF BETWEEN ABOUT 3AND ABOUT 8% BY WEIGHT OF THE IIRON ORE, WITH SAID SLEEVE-SHAPEDBRIQUETTE HAVING AT LEAST OONE GENERALLY VERTICAL PASSAGE THERETHROUGH,AND SAID BRIQUETTE FURTHER HAVING DEFINED IN AT LEAST ONE END THEREOF APLURALITY OF NOTCHES; ARRANGING A PLURALITY OF SAID SLEEVE-SHAPEDBRIQUETTES ON A MOVING TABLE OF ADI DIRECT-FIRED FURNACE WITH SAIDBRIQUETTES ARRANGED IN AN AXIALLY UPRIGHT POSITION AND WITH THE NOTCHEDENDS THEREOF ON SAID TABLE AND WITH PASSAGE EXTENDING VERTICALLYUPWARDLY; AND SUBJECTING SAID BRIQUETTES DIRECTLY TO FURNACE GASES AT ATEMPERATURE OF BETWEEN ABOUT 2000* AND ABOUT 2400* F. FOR A PERIOD OFTIME BETWEEN ABOUT 20 AND 35 MINUTES, THEREBY TO DIRECTLY REDUCE ASUBSTANTIAL PORTION OF THE METALLIC IRON OXIDE TO FREE IRON; WHILE SAIDMOVING TABLE CARRYING SAID BRIQUETTES SLOWLY ROTATES THROUGH THE FURNACEAND REMOVING SAID REDUCED BRIQUETTES FROM SAID FURNACE AND COOLING THEBRIQUETTES TO A TEMPERATURE OF ABOUT 200*F. OR BELOW IN A NONOXIDIZINGATMOSPHERE.
 2. A method as defined in claim 1 wherein the volume ratioof reducible mixture to open passage in said shaped briquette is about1-to-1.
 3. A method as defined in claim 1 wherein the proportion ofreducible mixture in said shaped briquette is between about 45% andabout 65% by volume.
 4. A method as defined in claim 1 wherein saidshaped briquettes include a plurality of apertures cut radially throughthe walls of each briquette intermediate its ends.
 5. A method asdefined in claim 1 wherein each said prismatic sleeve-shaped briquetteis annular in cross section.
 6. A method as defined in claim 1 whereineach said prismatic sleeve-shaped briquette is generally rectangular incross section.
 7. A method as defined in claim 1 wherein each saidsleeve-shaped briquette comprises a generally cylindrical member havinga height-to-outside diameter ratio of between about 1-to-1 and about2-to-1, an inside diameter of at least about 1/2 inch, and a wallthickness of between about 3/8 inch and about 1 inch, and said memberhaving defined in at least one end thereof a plurality of radiallyextending notches.
 8. A method as defined in claim 1 wherein each saidsleeve-shaped briquette comprises a generally rectangular member havinga plurality of vertically extending passages extending therethroughbetween the top and bottom thereof, said member having a volume ratio ofreducible mixture to passage volume of about 1-to-1 and a wall thicknessof between about 3/4 inch and about 1/18 inch, and said member havingdefined in one end thereof a plurality of notches extending through themember walls.
 9. A method of producing free metal by direct reduction ofa mixture containing a metallic oxide ore, comprising the steps offorming a prismatic sleeve-shaped briquette from a mixture of metallicoxide ore, a solid reducing agent and a binder, with said sleeve-shapedbriquette having at least one generally vertical passage therethrough,and said briquette further having defined in at least one end thereof aplurality of notches; arranging a plurality of said briquettes on acircular table of a direct-fired furnace with said briquettes in anaxially upright position, with the notched ends thereof on the furnacetable, and said passage extending vertically upwardly; and subjectingsaid briquettes directly to the furnace gases at a temperature below thesintering temperature of the free metal for a period of time sufficientto substantially reduce the metallic oxide to free metal while saidcircular table carrying said briquettes slowly rotates through thefurnace.
 10. A method producing free metal by direct reduction of ametallic oxide ore as defined in claim 9 including the step of coolingthe directly reduced briquettes in a nonoxidizing atmosphere to atemperature below that at which the free metal will be oxidized in air.